TheGreekMythosGuru

To simplify things, both Olympians and Titans will be considered Gods, representing different factions—similar to the Aesir and Vanir in Norse mythology. This approach makes it easier to keep track of the characters. For instance, Hecate is a Titan who eventually becomes a Goddess of Olympus.

Indeed.

As for entering the Underworld, that will work the same way with the river Styx passing through all the sections of the Underworld, carrying souls to Hades before being brought to their selected locations.

Yeah, it's just Hades accepting the Power of The Underworld, Zeus doing the same with the sky, and eventually, Poseidon with that Sea.

It's more like six pocket dimensions linked to one another rather than one continuous landscape.

they can be as tall or short as they want, usually depending on who they're fighting or seducing.

because they can be destroyed.

hestia isn't a fighter and hera loses in pretty much every one of her plots whilst demeter literally nearly destroys the world in her rage and athena is the wisest being in existence and arguably zeus strongest child.

when in the underworld yea, he pretty much can't be beat there. similarly, neither can poseidon in the sea nor zeus in the sky. depending on whether or not the person whose attacking them has a connection to their domain or not.